Method of detecting objects within range of a receiver

• US 6,727,810 B1
• Filed: 10/12/1999
• Issued: 04/27/2004
• Est. Priority Date: 10/12/1999
• Status: Expired due to Term

• Current Assignee: Xmark Corporation (Stanley Black & Decker, Inc.)
• Original Assignee: Instantel, Inc. (Positiveid Corporation)
• Inventors: Martin, Brian, McKenzie, Jennifer
• Primary Examiner(s): POPE, DARYL C
• Application Number:
  US09/416,534
• Time in Patent Office: 1,659 Days
• Field of Search: 340/506, 340/505, 340/539.1, 340/539.11, 340/539.12, 340/539.13, 340/539.15, 340/572.1, 340/573.4, 340/3.1, 340/3.21, 340/3.41, 340/3.5, 340/3.51, 340/825.2, 340/10.1, 340/10.2, 340/286.07, 340/572.4, 340/10.41
• US Class Current: 340/506
• CPC Class Codes: G08B 13/2462 Asset location systems combined with EAS inventory, tracking, logistic G06Q10/00; entrance control systems G07C9/00
• CPC Class Codes: G08B 13/2488 Timing issues, e.g. synchronising measures to avoid signal collision, with multiple emitters or a single emitter and receiver
• CPC Class Codes: G08B 26/007 Wireless interrogation

Abstract

A method of detecting a variable number of objects within range of a receiver, is comprised of transmitting from each object a supervisory message from time to time, detecting the supervisory message by the receiver over a detection interval, and varying the detection interval based on a number of objects under supervision and the probability of collisions of the supervisory messages.

Claims

1. A method of detecting a variable number of objects within range of a receiver, comprising:

(a) transmitting from each object a supervisory message from time to time;

(b) detecting the supervisory message by the receiver over a detection interval;

(c) dynamically varying the detection interval based on a number of objects under supervision and the probability of collisions of the supervisory messages;

(d) increasing the detection interval to the extent that no collisions of any previously undetected supervisory message occurs; and

(e) raising an alarm in the event a supervisory message of a previously detected object is not detected within the detection interval.

2. A method as defined in claim 1 including randomly transmitting the supervisory messages from various objects.

3. A method as defined in claim 2 including keeping track of the number of tags in a detection region of a receiver by determining an average number of supervisory messages over a predetermined time period.

4. A method as defined in claim 2 including keeping track of the number of tags in a detection region of a receiver by maintaining a table of unique Ids of respective objects from Ids transmitted In the supervisory messages.

5. A method as defined in claim 1 including controlling the receiver from a control computer, and determining the detection interval for such control by the control computer.

6. A method as defined in claim 1 including plural ones of said receivers each having an object detection region which overlaps the detection region of a neighboring receiver, and repeating steps (a), (b), (c) and (d) for each receiver.

7. A method as defined in claim 6 including controlling the receivers from a control computer, and determining various detection intervals of the respective receivers by the control computer.

8. A method as defined in claim 7 including raising an alarm in the event the supervisory message from an object detected by more than one receiver is not detected within a detection interval which is the shortest used by said more than one receiver.

9. A method as defined in claim 1 in which the objects are attachments to physical structures or living entities.

10. A method as defined in claim 1 in which the objects are located on or adjacent the surface of the earth and in which the receiver is located in an earth satellite.

11. A method as defined in claim 1 in which the objects are located in plural earth satellites, and in which the receiver is located on or adjacent the surface of the earth.

13. A method as recited in claim 1 wherein each object is capable of transmitting but not receiving.

12. A method of detecting a variable number of objects within range of a receiver, comprising:

(a) transmitting from each object a supervisory message from time to time;

,

(b) detecting the supervisory message by the receiver over a detection interval;

(c) dynamically varying the detection interval based on a number of objects under supervision and the probability of collisions of the supervisory messages;

(d) Increasing the detection interval to the extent that no collisions of any previously undetected supervisory message occurs;

(e) providing plural ones of said receivers each having an object detection region which overlaps the detection region of a neighboring receiver, and repeating steps (a), (b), (c), and (d) for each receiver;

(f) controlling the receivers from a control computer, and determining various detection intervals of the respective receivers by the control computer; and

(g) raising an alarm in the event the supervisory message from an object detected by more than one receiver is not detected within a detection interval which is the shortest used by said more than one receiver.

14. A method as recited in claim 12 wherein each object is capable of transmitting but not receiving.

15. A method as recited in claim 12 including randomly transmitting the supervisory messages from various objects.

16. A method as recited in claim 15 including keeping track of the number of tags in a detection region of a receiver by determining an average number of supervisory messages over a predetermined time period.

17. A method as recited in claim 15 including keeping track of the number of tags in a detection region of a receiver by maintaining a table of unique Ids of respective objects from Ids transmitted in the supervisory messages.

18. A method as defined in claim 12 in which the objects are attachments to physical structures or living entities.

19. A method as defined in claim 12 in which the objects are located on or adjacent the surface of the earth and in which the receiver is located in an earth satellite.

20. A method as defined in claim 12 in which the objects are located in plural earth satellites, and in which the receiver is located on or adjacent the surface of the earth.